The rapid development of the rubber and resin industry leads to an evergrowing demand for butadiene in the market. Notwithstanding 1,3-butadiene obtained from naphtha cracking process accounts for 90% of the total production of butadiene, the shortage of the butadiene required has to be covered by oxydehydrogenation of butene due to the domestic limitation of the naphtha output and the cracking units.
Synthesis of butadiene in an industrial scale may be conducted by dehydrogenation or oxydehydrogenation of butene at present. Direct dehydrogenation of butene is a strong endothermic reaction requiring high temperature and low pressure conditions, which suffers from low yield and difficulty in commercialization. In contrast, oxydehydrogenation of butene produces butadiene and water. It is a strong exothermic reaction, and thus the reaction temperature may be decreased appropriately.C4H8→C4H6+H2 ΔH298 K, 1 MPa=113.6 kJ·mol−1 C4H8+½O2→C4H6+H2O−ΔH298 k, 1 MPa=127.9 kJ·mol−1 
Industrial production of butadiene is carried out by passing a mixed C4 feedstock, steam and air through a fixed or fluidized bed in the presence of a catalyst to produce butadiene. Since the oxydehydrogenation of butene is a strong exothermic reaction, while removal of heat from a fixed bed reactor is difficult, excessive increase of temperature in the catalyst bed is resulted, which is undesirable for temperature control. For a traditional fixed bed reactor used for oxydehydrogenation of butene, a temperature difference of 150-250° C. exists between the teed port and the discharge port, and two reactors, one in preparation and the other in operation, are needed.
In a fluidized bed reactor, the heat produced by oxydehydrogenation of butene can be removed easily, and operation at constant temperature may be realized. Consequently, the catalyst life can be extended, and the catalyst usability can be improved. Moreover, owing to its relatively simple structure, a fluidized bed reactor is easy to manufacture and process, facilitating its industrial scale-up. However, an industrial fixed bed catalyst for oxydehydrogenation of butene cannot be applied to a fluidized reactor for reasons of shape, mechanical strength, wear resistance, etc. It is critically important to synthesize a catalyst which not only is suitable for oxydehydrogenation of butene in a fluidized bed, but also has good wear resistance, high activity, long-term stability in operation, etc.
CN 1184705A and CN1072110A disclose an iron-based catalyst for the preparation of butadiene by oxydehydrogenation of butene. Although this catalyst shows some activity and/or selectivity when used in a baffled fluidized bed, the yield of butadiene is rather low, and severe loss of the catalyst is witnessed, because the catalyst has irregular shape and large particle size. The SEM image of the irregularly shaped catalyst is shown in FIG. 1.
CN101674883 discloses a process for preparing 1,3-butadiene using a zinc ferrite catalyst, wherein a composition comprising zinc ferrite is used, and it's difficult to achieve an ideal catalytic effect. Furthermore, this catalyst is used in a fixed bed reactor. The temperature at the catalyst bed is increased unduly, and the energy consumption is high. Similarly, the wear problem of the catalyst in the fixed bed reactor can not be solved either.
U.S. Pat. No. 8,003,840B2 discloses a process for preparing 1,3-butadiene using a series of bismuth molybdenate catalysts. This series of catalysts are used in a fixed bed reactor, and the problems of wear resistance and high mobility of the catalysts are not solved. Moreover, the catalyst only has moderate catalytic activity.